The present application claims the benefit of prior filed China Applications, serial numbers 98 2 29711.4 and 98 2 29712.2, both filed Oct. 21, 1999 to which the present application is a regular U.S. national application.
The present invention is in the field of sterilizable cultivation containers for growing selected organisms in isolation from the ambient environment. More specifically, it relates to a microfiltration membrane that is separately adhereable to a sterilizable cultivation container. In particular, the present invention relates to such containers for the cultivation of edible fungi.
Aerobic organisms during growth require oxygen and produce carbon dioxide. In order to grow and maintain a pure strain of a selected organism, it is advantageous to exclude competing organisms, including microorganisms, from the growth environment as well as maintain the proper oxygen to carbon dioxide ratio. Sterilizable cultivation containers provide this advantage. Such containers are used extensively for the cultivation of edible mushrooms. Much of this cultivation is accomplished using plastic pouches or bags. However, the cost of bags and pouches can represent a high percentage of total raw material cost, which encourages the recycling of the bags and pouches. In order to provide proper venting when using recycled cultivation containers, growers often resort to cotton vent plugs, which are inherently less reliable or controllable than desired.
Control of the internal growing environment of the cultivation container is important, and the field has been motivated to address this issue. For example, U.S. Pat. No. 5,230,430, noting that it is desirable to maintain moisture content, attempts to provide a method for moisture control. However, the ""430 patent does not teach a means for modifying the moisture conditions once the container is in use in the field to increase moisture loss. Also, the manufacture of the container of the ""430 patent is complicated in that it requires the integration of a filter element into an otherwise ordinary plastic bag during the course of manufacture of the bag. Also, because of the integrated filter element of the ""430 bag and similar cultivation containers, the ability to recycle containers is reduced.
It would be beneficial to have a sterilizable cultivation system wherein the moisture loss can be controllably increased or decreased in the field. Additionally, it would be advantageous to be able to use ordinary manufactured plastic bags as cultivation containers, and to be able to recycle them.
The present application claims the benefit of prior filed China Applications, serial numbers 98 2 29711.4 and 98 2 29712.2, both filed Oct. 21, 1999, the content of which are incorporated herein by reference.
The present invention is a sterilizable cultivation system for growing a homogeneous population of a selected organism on a growth supporting substrate. The system is useful in agricultural and biological applications where isolation of the growing organism from the general environment is desirable. The system is advantageous for preventing contamination of the growing organisms from competing organisms present in the environment, and for preventing exposure to the environment from the organisms being cultivated. The present cultivation system is particularly useful for the growing of edible mushrooms, but is useful also for the growth of other fungi, nematodes, and similar organisms that are desirable to grow in isolation.
The present invention comprises a sealable container, the interior of which holds a substrate suitable for growing the selected organism after it is inoculated onto the substrate. The container is capable of holding the substrate in a sterile condition, meaning that: (a) sterile substrate can be added to the container and kept sterile, or (b) substrate can be added to the container and subsequently made sterile. The container itself should be relatively impervious to the ambient environment and substantially gas impermeable. In order to support the growth of aerobic organisms, the container has at least one vent or breathing hole to allow gas exchange between the interior of the container and the ambient environment outside of the container. A separate breathing filter is adhered to the container to cover the vent/breathing hole. The filter allows gas transmission or exchange of gases between the interior of the container and the ambient environment, while not allowing passage or transmission of microbes. A layer of a non-water soluble, pressure sensitive adhesive is posited between the container and the breathing filter. The adhesive layer provides for closely adhering the filter to the container, thus isolating the vent hole and interior of the container from the ambient environment.
The breathing filter is typically constructed in a flat or planar configuration, and has a central area and a periphery. The peripheral area is for receiving or contacting the adhesive layer when adhering the filter to the container, and the central area is for gas exchange and filtration. The vent holes in the container are to covered individually or in multiples using one or more breathing vent filters. The filters are provided separately from the container, as individual unit items or in multiples, such as where multiple breathing filters are arranged at their periphery, as in a series or an array, and wound into a roll or provided in sheets. The filters can be individually removed from a sheet or roll for adhering to the container. This allows the filters to be placed on the container by the end-user in the field. In this way, the end user may recycle the container for more than one cultivation cycle. Die-cuts and perforations or the like can be provided in the filter material to facilitate removing individual filters from a roll or sheet.
The breathing filter includes a microfiltration membrane. The microfiltration membrane has micron and smaller sized pores or breathing holes to excludes microbes (including fungi and bacteria) from passing into or out of the container. The breathing pore holes range in size from about 1.0 xcexcm to 0.05 xcexcm in diameter. Preferably, the breathing pores are evenly distributed on the micro filter breathing membrane, and preferably range from about 1.0 xcexcm to 0.3 xcexcm in diameter. The amount of the breathing filter""s central area available for gas exchange and filtration is modifiable by covering the microfiltration membrane with an occlusive agent (such as adhesive tape, paint or the release paper).
The adhesive layer of the present invention is made of a pressure sensitive adhesive for closely adhering the breathing filter to the container. In order to facilitate recycling of the container, it is desirable that the adhesive layer be releaseable from the container. Also, for some applications, it is desirable that the adhesive used in the adhesive layer is both releaseable from and re-adhereable to the container. Appropriate adhesives having these qualities are known to and selectable by one of ordinary skill in the art of adhesives. The advantage of an adhesive layer that is both releaseable from and re-adhereable to the container is that inoculation of sterile substrate held in the container with a selected organism can be accomplished through the vent hole without substantial compromise of the sterility of the cultivation system.
The adhesive layer is covered by a release material, which is removable from the adhesive layer prior to adhering the filter to the container. Such release materials include silicone release paper, a release coating and other adhesive release means known to one of ordinary skill in the art. When the adhesive layer is combined with the breathing filter, it is applied or coated only on the periphery of the filter, in a wide enough pattern to assure close adhesion of the filter to the container.
The separate breathing filter of the present invention may be constructed as a laminate of a microfiltration membrane and a support material, to help protect the membrane and to give the breathing filter added strength and durability. The support material can be made of any of a number of openly porous materials known to the ordinary skilled artisan, including polymer based, cellulose based or other fiber based or non-woven materials. The adhesive layer can be applied directly to the breathing filter laminate as described above. Alternatively, the periphery of the vent hole in the container can provide a surface area for contacting the adhesive layer. In this case, the adhesive layer is applied to the container separately from the breathing filter, and is protected prior to use with a release paper or similar means as disclosed above.
An individual filter laminate may include a central area of variable size. The user can peel off increasingly larger concentric, pre-scored areas of adhesive to expose similarly larger central areas of the microfiltration membrane.
The sterilizable cultivation system of the present invention anticipates that the sealable container may take a variety of constructions in that it may be rigid, semi-rigid or very flexible. Likewise, it may have a variety of configurations, such as a bag, a cylinder, bottle or box. Preferably, the container is a bag formed from a length of flexible tubular material and sealable at both ends to provide a sealable container. In order to accomplish the bag being recyclable, at least one of the sealable ends is un-sealable and re-sealable, allowing the bag to be re-used. For the growing of mushrooms and the like where the ability to inspect the contents of the container is desirable, the container can be made of clear or semi-transparent materials.
The exact composition of the growth substrate of the present invention is dependent on the selected organism it is desirable to cultivate. Generally, the starting substrate is a mixture of solid particles and nutrients suitable for growing the selected organism.